In all standard film contracts, amidst the verbiage that surrounds the interesting paragraph about remuneration, there nestles a commitment that, I suspect, few actors read before signing. Only when the filming is done and the release date approaches comes the realisation of what, months before, was agreed to  a promise, if free of other professional work, to participate in the business of publicising the movie.

How much of this is actually required will depend upon the actor's individual status. To a junior, unknown actor, for instance, attending a "junket" (i.e. meeting the media en masse over a day or two or three) can seem the very stuff of glamour; and television, radio and press interviews, the enviable terrain of stardom. But when I found myself in Berlin one weekend in 1996 publicising Richard III, a film which I had instigated and starred in, I experienced the reality  75 interviews, short and long, over three days, and a subsequent headache that lasted for a week. When I was then despatched alone on a 13-city (sometimes two in a day) tour across the United States talking to the local media, you might think I would have learned that glamour and publicity don't belong in the same sentence. Junkets are events to be avoided  but there is always that contractual obligation.

Yet when New Line "invited" me to the annual Cannes Film Festival in May, I was happy to accept. Apart from anything else, it would be fun to reunite with the Fellowship and the Jacksons, who were having a rare separation from their kids. I had been to Cannes only once before, again on Richard III business, in a fruitless quest for finance. Despite the competition and the new films, Cannes is more a market than a festival. Hotel rooms are transformed into displays peddling unmade films that need funds, and completed ones that need a buyer. Business transactions go on late into the night in hotel bars and pricey restaurants out of sight of the public.

Over three days, the sun shone on a massive balloon in the shape of Arnold Shwarzenegger, which was tethered out in the bay amongst the millionaire's yachts. I accompanied Elizabeth Taylor at a press conference about AIDS, narrowly avoiding permanent eye damage as 500 cameras flashed at her everlasting beauty. Whatever happens to those photographs? It's the same at the Oscars' ceremony  miles of film shot along the red carpet and next day every paper seems to carry the same picture as if it were the only one that had been taken.

This year at Cannes, coinciding with a local holiday, tourists kept a constant vigil four-deep around the main hotels along the curved seafront (La Croisette). Their cameras at the ready, they never seemed to care when I passed them by and that's fine with me. I kept my eyes open too but stars were thin on the Croisette this year, apart from the Lord of the Rings cast.

We met up first at the downtown cinema where we were to be shown, ahead of the distributors and selected media, the first completed footage from the trilogy. Extra sound equipment was installed to ensure the full Dolby onslaught. I sat near the back, next to Saruman and Mrs Lee, with Frodo in front of me. Peter Jackson and Bob Shaye, New Line's supremo, welcomed us and warned us that not everything we would see was entirely finished. They could have fooled me.

The lights dimmed and the sequence opened with Gandalf's cart pulling up to the gate of Bag End - the first shot I had filmed 16 months earlier. Bilbo answered the door and the camera pushed into the hobbit hole. How big Gandalf looked as he dodged the low ceiling! By what film magic I now forget, he casually handed over his pointy hat and staff. How small Bilbo looked as he staggered with them along the hall! This disparity of size goes unremarked when reading Lord of the Rings but, of course, on screen it is unavoidable. Watching yourself act is unnerving, sometimes akin to viewing the holiday snaps and realising how unfortunate that summer outfit was or how unflattering that long-abandoned hairstyle. With relief and some excitement I can report that Peter Jackson's images not only look convincing they look stunning  like an Alan Lee picture book come to life. That goes for all the actors' performances and the non-actors too, now I've seen the cave troll and Balrog deep in the Moria mines. The Moria extract ended with Gandalf's "You shall not pass!" followed by some tempting bits from the second and third films. We shamelessly applauded ourselves. The Hobbit actors whooped. And Elijah asked to see it all over again.

Next day work started. In the hills above Cannes a modernised ancient castle had been prepared for the junket. The actors were split into threes to talk to the press. I was put between Orlando Bloom and John Rhys-Davies and we toured round a dozen groups of 15 or so journalists who asked questions and recorded them on their tape recorders. Most of the questions were very similar and so we began to repeat our answers group by group.

This pattern worsened the next day when we talked on television. This time it was the journalists who toured. Under a large cotton canopy protecting us from the sun's heat, I sat for seven hours between Ian Holm and Christopher Lee as at five-minute intervals we were joined by a progression of interviewers from all over the globe, their brief sessions recorded by two static video cameras. Each of them, charmingly, referred to our age: "Ah now here I am with The Three Veterans in the cast. Between them they have more than 150 years' experience! How fit you look gentlemen!" To these unintentional insults, Chris was unfailingly gallant and magnificently fluent in not only half a dozen European languages (well, Mrs Lee is Danish and he is half-Italian) but also a smattering of small talk from the other four continents. Agog the two Ians were introduced to Afrikaans, Zulu, Japanese, Mandarin Chinese, Swahili and more. I couldn't manage anything more foreign than "Bon Jour" and "Ciao". We were amused to be so eruditely upstaged.

Perhaps to prove that he too was capable of more than the routine answers with which we responded to the repetitious questions, toward the end of the afternoon, without warning Ian Holm launched into a reply which he'd never given before and as I listened, the ludicrous side of the day impinged on my funny bone. It was like hearing a colleague on stage deliberately diverting from the text he has repeated night after night during a long run. And so I started to laugh. First I just smiled and then giggled to myself, just in control, biting my lip so as not to be noticed  after all how to explain that the sun had finally started to turn my brain? Then exhaustion released my self-control and I began to laugh. And laugh out loud. Ian continued talking. So I laughed some more, carefree and enjoying it now. I stood up and rocked on my feet roaring by this time, until all I could was to run away, laughing across the lawn in search of a drink. Chris told me later that he feared for my sanity. He was right to.